OK, so suppose we have an observer. Now look at the cat. Is it alive or dead? If it is alive and only alive, well, we can affix the phrase “relative to the observer” but it doesn’t diminish the absoluteness of the cat’s being alive. But if the cat is alive “relative to one observer to which it is alive”, and dead “relative to another observer to which it is dead”, how can we possibly make sense of that except in many-worlds fashion, by saying there are two cats and two observers?
If two observers measure a cat, they will get compatible results. However one observer can have less complete information (“the cat collapsed”) and another more complete (“the cat is uncollapsed”). Observers can disagree about “collapse” because that is just an issue of their information, not an objective property.
“Relational interpretation
The relational interpretation makes no fundamental distinction between the human experimenter, the cat, or the apparatus, or between animate and inanimate systems; all are quantum systems governed by the same rules of wavefunction evolution, and all may be considered “observers.” But the relational interpretation allows that different observers can give different accounts of the same series of events, depending on the information they have about the system.[11] The cat can be considered an observer of the apparatus; meanwhile, the experimenter can be considered another observer of the system in the box (the cat plus the apparatus). Before the box is opened, the cat, by nature of it being alive or dead, has information about the state of the apparatus (the atom has either decayed or not decayed); but the experimenter does not have information about the state of the box contents. In this way, the two observers simultaneously have different accounts of the situation: To the cat, the wavefunction of the apparatus has appeared to “collapse”; to the experimenter, the contents of the box appear to be in superposition. Not until the box is opened, and both observers have the same information about what happened, do both system states appear to “collapse” into the same definite result, a cat that is either alive or dead.”—WP
In the interpretation of QM, one of the divides is between ontic and epistemic interpretations of the wavefunction. Ontic interpretations of the wavefunction treat it as a thing, epistemic interpetations as an incomplete description or a tabulation of uncertainty, just like a probability distribution.
In the relational interpretation of QM, are the states understood as ontic or as epistemic? The passage you quote makes them sound epistemic: the cat knows but the observer outside the box doesn’t, so the observer outside the box uses a different wavefunction. That undoubtedly implies that the wavefunction of the observer outside the box is epistemic, not ontic; the cat knows something that the outside observer doesn’t, an aspect of reailty which is already definite even though it is not definite in the outside observer’s description.
Or at least, this ought to imply that quantum state in the relational interpretation are epistemic. However, this is never explicitly stated, and instead meaningless locutions are adopted which make it sound as if the quantum states are to be regarded as ontic, but “relative”.
There are certain very limited senses in which it makes sense to say that the state of something is relative. For example, we may be floating in space, and what is up to you may be down to me, so whether one object is above another object may be relative to an observer. But clearly such a dodge will not work for something like Schrodinger’s cat. Either the cat is alive, dead, both, or neither. It can’t be “alive for one observer and dead for another” and still be just one cat. But that is the ontological implication one gets, if “relational QM’ is interpreted as an ontic interpertation.
On the other hand, if it is an epistemic interpretation, then it still hasn’t answered the question, “what is the nature of reality? what is the physical ontology behind the formalism and the instrumental success?”
It can’t be “alive for one observer and dead for another”
It can’t in rQM:
“However, the comparison does not lead to contradiction because the comparison is itself a physical process that must be understood in the context of quantum mechanics. Indeed, O′ can physically interact with the electron and then with the l.e.d. (or, equivalently, the other way around). If, for instance, he finds the spin of the electron up, quantum mechanics predicts that he will then consistently find the l.e.d. on (because in the first measurement the state of the composite system collapses on its [spin up/l.e.d. on] component). That is, the multiplicity of accounts leads to no contradiction precisely because the comparison between different accounts can only be a physical quantum interaction. This internal self-consistency of the quantum formalism is general, and it is perhaps its most remarkable aspect. This self consistency is taken in relational quantum mechanics as a strong indication of the relational nature of the world”—SEP
OK, so suppose we have an observer. Now look at the cat. Is it alive or dead? If it is alive and only alive, well, we can affix the phrase “relative to the observer” but it doesn’t diminish the absoluteness of the cat’s being alive. But if the cat is alive “relative to one observer to which it is alive”, and dead “relative to another observer to which it is dead”, how can we possibly make sense of that except in many-worlds fashion, by saying there are two cats and two observers?
If two observers measure a cat, they will get compatible results. However one observer can have less complete information (“the cat collapsed”) and another more complete (“the cat is uncollapsed”). Observers can disagree about “collapse” because that is just an issue of their information, not an objective property.
“Relational interpretation
The relational interpretation makes no fundamental distinction between the human experimenter, the cat, or the apparatus, or between animate and inanimate systems; all are quantum systems governed by the same rules of wavefunction evolution, and all may be considered “observers.” But the relational interpretation allows that different observers can give different accounts of the same series of events, depending on the information they have about the system.[11] The cat can be considered an observer of the apparatus; meanwhile, the experimenter can be considered another observer of the system in the box (the cat plus the apparatus). Before the box is opened, the cat, by nature of it being alive or dead, has information about the state of the apparatus (the atom has either decayed or not decayed); but the experimenter does not have information about the state of the box contents. In this way, the two observers simultaneously have different accounts of the situation: To the cat, the wavefunction of the apparatus has appeared to “collapse”; to the experimenter, the contents of the box appear to be in superposition. Not until the box is opened, and both observers have the same information about what happened, do both system states appear to “collapse” into the same definite result, a cat that is either alive or dead.”—WP
In the interpretation of QM, one of the divides is between ontic and epistemic interpretations of the wavefunction. Ontic interpretations of the wavefunction treat it as a thing, epistemic interpetations as an incomplete description or a tabulation of uncertainty, just like a probability distribution.
In the relational interpretation of QM, are the states understood as ontic or as epistemic? The passage you quote makes them sound epistemic: the cat knows but the observer outside the box doesn’t, so the observer outside the box uses a different wavefunction. That undoubtedly implies that the wavefunction of the observer outside the box is epistemic, not ontic; the cat knows something that the outside observer doesn’t, an aspect of reailty which is already definite even though it is not definite in the outside observer’s description.
Or at least, this ought to imply that quantum state in the relational interpretation are epistemic. However, this is never explicitly stated, and instead meaningless locutions are adopted which make it sound as if the quantum states are to be regarded as ontic, but “relative”.
There are certain very limited senses in which it makes sense to say that the state of something is relative. For example, we may be floating in space, and what is up to you may be down to me, so whether one object is above another object may be relative to an observer. But clearly such a dodge will not work for something like Schrodinger’s cat. Either the cat is alive, dead, both, or neither. It can’t be “alive for one observer and dead for another” and still be just one cat. But that is the ontological implication one gets, if “relational QM’ is interpreted as an ontic interpertation.
On the other hand, if it is an epistemic interpretation, then it still hasn’t answered the question, “what is the nature of reality? what is the physical ontology behind the formalism and the instrumental success?”
It can’t in rQM:
“However, the comparison does not lead to contradiction because the comparison is itself a physical process that must be understood in the context of quantum mechanics. Indeed, O′ can physically interact with the electron and then with the l.e.d. (or, equivalently, the other way around). If, for instance, he finds the spin of the electron up, quantum mechanics predicts that he will then consistently find the l.e.d. on (because in the first measurement the state of the composite system collapses on its [spin up/l.e.d. on] component). That is, the multiplicity of accounts leads to no contradiction precisely because the comparison between different accounts can only be a physical quantum interaction. This internal self-consistency of the quantum formalism is general, and it is perhaps its most remarkable aspect. This self consistency is taken in relational quantum mechanics as a strong indication of the relational nature of the world”—SEP